CHAPTER SEVEN – CHEMICAL FORMULAS SOUTH LAKE HIGH SCHOOL SCIENCE DEPARTMENT MS. SANDERS Chemistry

Naming Ions Ions Cation – positive charge Anion – negative charge Monatomic ions – ions formed from a single atom Polyatomic ions – ions formed from more than one atom

Naming Ions Polyatomic Ions:  Ammonium - NH ₄⁺¹  Acetate - CH₃COOˉ¹  Chlorate - ClO₃ˉ¹  Cyanide - CNˉ¹  Hydroxide - OHˉ¹  Nitrate - NO₃ˉ¹  Carbonate - CO₃ˉ²  Sulfate - SO₄ˉ²  Phosphate - PO₄ˉ³

Naming Compounds Ionic Compounds:  Name cation first  Anion ends in –ide  For writing formulas, look at group to get the charges Practice page 227:  1b) calcium chloride  1e) copper (II) sulfate  2a) Ag ₂O  2b) Ca(OH)₂  2c) KClO₃

Naming Compounds Molecular Compounds:  Look at prefix (page 228); mono- 1, di- 2, tri- 3, and so on  Also ends in -ide Practice Page 229:  1a) SO ₃  1c) PBr ₅  2a) carbon tetraiodide  2c) dinitrogen trioxide

Oxidation Numbers Used to keep track of the overall electron distribution In bonded atoms or polyatomic ions Oxidation numbers are assigned to the atoms Need to learn the rules on page 232

Oxidation Numbers Rules:  Pure element = 0  Binary molecular compound = charge  Fluorine = -1  Oxygen = -2, sometimes +2  Hydrogen = +1, except with metals = -1  The sum of the numbers must equal 0 in a neutral atom  The sum of the numbers must equal the charge of an ion  Monatomic ions = charge

Oxidation Numbers Practice Page 234:  1a) HCl  1b) CF ₄  1c) PCl₃  1d) SO₂  1e) HNO₃  1f) KH  1g) P₄O₁₀  1h) HClO₃

Formula and Molar Mass Get from the periodic table Formula mass – amu Molar mass – g/mole Add mass together Examples:  H ₂SO₄  Ca(NO₃)₂

Formula and Molar Mass Convert grams to moles (review):  Given x unknown = unknown Practice page 242:  How many moles are in 6.6 g (NH ₄)₂SO₄?

Empirical Formula Subscripts showing smallest whole-number mole ratio Steps:  % composition is the mass (g)  Convert mass to moles (use molar mass)  Moles to smallest ratio (divide by smallest mole)

Empirical Formula Practice page 247  Find empirical formula: 63.52% Fe and 36.48% S

Empirical Formula Practice page 247  Find empirical formula: 26.56% K, 35.4% Cr, and 38.03% O

Percent Composition % comp =(mass element/mass compound) x 100 Practice page 244:  PbCl ₂ What is the percent composition?